Electromechanical intervalometer, and method of using same

ABSTRACT

Apparatus and method for effecting firing, at predetermined intervals, of rockets, flares or the like. An astable, asymmetrical multivibrator oscillator is adapted to maintain energized, during the major portion of each cycle of oscillation, a solenoid which operates a stepping switch connected to the rockets. The multivibrator is adapted to complete a firing circuit through the stepping switch during the remaining or minor portion of each oscillatory cycle. The relative lengths of the cycle portions are so correlated to the firing times and shock wave-transmission times of the rockets that the solenoid is energized when the shock resulting from any firing reaches the stepping switch. The multivibrator is so constructed that pressing of the pilot-operated start button always effects initiation of operation of the long (major) portion of the cycle, but for only an abbreviated time period adapted to effect initial stepping of the stepping switch. An isolated power storage capacitor maintains operation of the multivibrator during temporary power dropouts.

Unite tates Patent 1151 3,700,97 1

Everest et al. 1 1 Oct. 24, 1972 [54] ELECTROMECHANICAL 3,571,605 3/1971 Dobson et al ..317/80 INTERVALOMETER, AND METHOD 3,316,451 4/1967Silberman ..3 17/80 OF USING SAME P' E B 1h [72] Inventors: Charles E.Everest, Los Angeles; g z gr 5 513 G1 eany Henry R vomick, Arcadia bothof AtzorneyGausewitz, Carr & Rothenberg Calif. 73 Assignee: William WahlCorporation, Los An- ABSTRACT geles, Calif- Apparatus and method foreffecting firing, at [22] Filed: Jam 29, 1971 predetermined intervals,of rockets, flares or the like. An astable, asymmetrical multivibratoroscillator is PP 111,048 adapted to maintain energized, during the majorportion of each cycle of oscillation, a solenoid which RelatedApplicat'on Data operates a stepping switch connected to the rockets.[63] Continuation-impart of Ser. No. 882,431, Dec. T mu tivi at s adaptt mp t a fir g cir- 5, 1969, ab d d, cuit through the stepping switchduring the remaining or minor portion of each oscillatory cycle. Therela- [52] US. Cl ..317/80, 89/ 1.814 live lengths of the cycle Portionsare correlated to 51 Int. Cl ..F23g 21/00 the firing times and shockwave-transmission times of 58 Field of Search ..317/80; 335/138; 102/91;the rockets that the Solenoid is energized when the 89/18, L807, 1.813,L314, 27, 28 15 shock resulting from any firing reaches the stepping315/214 216, 217 switch. The multivibrator is so constructed thatpressing of the pilot-operated start button always ef- [56] 1 ReferencesCited fects initiation of operation of the long (major) portion of thecycle, but for only an abbreviated time UNITED STATES PATENTS periodadapted to effect initial stepping of the stepping switch. An isolatedpower storage capacitor 2421893 6/1947 Lambert et E X maintainsoperation of the multivibrator during tem- 3,396,628 8/1968 Nash..s9/1.s14 d t 3,315,565 4/1967 Nash ..s9/1.s14 x pwer 3,453,496 7/1969Wright et al. ..s9/1.s14 x 50 Claims, 7 Drawing Figures ELECTROWCHANICALVALOMETER, AND WTHOD OF USING SAME REFERENCE TO RELATED APPLICATION Thisis a continuation-in-part of our co-pending ap plication, Ser. No.882,431, filed Dec. 5, 1969, now abandoned for Electromechanicalintervalometer, and Method of Using the Same.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the field of electromechanical devices, and associatedmethods, for controlling the firing of rockets or flares in apredetermined sequence and with predetermined times between firings.

2. Description of the Prior Art It is known to fire rockets from rocketlaunchers by means of intervalometers or stepping switches, the purposebeing to provide predetermined time intervals between the ignition ofvarious rockets or pairs of rockets. Each rocket (or rocket pair) isignited by supplying thereto an electric current, the current beingderived from the aircraft electrical system or from a military powersource on the ground. The current passes through a stepping switch orintervalometer the operation of which is initiated by manual closing ofa control switch by the aircraft pilot or vehicle commander, etc.

The firing of the rockets creates great shock, vibration and acousticaleffects in the rocket launcher, the result being that all elements inthe launcher, including the intervalometer, are subjected to extremelyheavy disturbing forces. Such forces are in turn amplified as eachadditional rocket or pair of rockets is fired. As a result of theseextreme forces, prior-art stepping switches or intervalometers have notbeen able to control the intervals between firings in any consistentmanner. The resulting variations cause the rockets to leave the launcherin such closely-spaced relationship that interference and damage to therockets sometimes occurs, and may even result in the breaking of partsoff the rockets. When the rockets are launched from aircraft, the brokenand flying parts may be ingested by the turbojet engines, withconsequent destruction of the aircraft. In addition, the erratic firingintervals, some of which are short and some long, have causedaerodynamic interferences with consequent reduction in the effectivenessof the fins of the rockets, so that the rockets become unstable andtherefore disperse over excessively wide regions.

The above problems are compounded by the fact that the intervalometermust-operate under a very wide variety of environmental conditions,including low temperatures ranging to 65 below zero (for aircraft flyingat high altitudes or in the Arctic zones), to high temperatures up to165 above zero. In addition, there are voltage variations, for examplein the range of from 20 to 30 volts, which must be contended with.

It will thus be seen that the extreme environmental conditions to whichthe intervalometer is subjected prior to firing are compounded by thevibratory shocks which result from firing, creating an overall conditionwhich is severe in the extreme. It is therefore desired to provide anapparatus which will produce discrete timed intervals for firing rocketswhile in the launcher, which is insensitive to the shocks, vibrationsand acoustics developed by the rockets when launched, and whichaccordingly will continue to provide the necessary control pulses atrepeatable, controlled intervals determined by presettings at thefactory or in the field.

The military requirements of an electromechanical intervalometerincorporating electronic components are particularly severe since theelectronic components must fit into an extremely small space, namely,the space previously required by an intervalometer not incorporatingelectronic components.

One of the major factors which has heretofore prevented the creation ofa practical electromechanical intervalometer, incorporating electronicelements, is that the first firing pulse must be delivered only a veryshort time period after the pilot or commander presses the button. Thisis particularly difiicult to achieve in conjunction with relaxationoscillators, and without employing excessive numbers of components,since normally the capacitors in such oscillators require substantialcharging times which prevent delivery of firing pulses until a ratherlong time interval after the start button is pressed.

Examples of prior-art intervalometers, and which do not incorporateelectronic elements, are described in Davis US. Pat. No. 3,384,728 andGiese U.S. Pat. No. 3,405,376. lntervalometers of this and similar typesincorporate interrupter switches which may be either single-throw ordouble-throw in nature. In such intervalometers or stepping switches,the power to the solenoid is only applied during a minor portion of thetime, such minor portion being barely sufficient to effect retraction ofthe armature. Because of the short durations of the periods during whichpower is applied to the solenoid, and because of various other factorsincluding contact bounce in the interrupter switch, and also includingthe severe environmental conditions mentioned above, the types ofintervalometers shown in these patents were characterized by erraticfiring and by other defects and deficiencies.

A prior-art electromechanical intervalometer incorporating electronicelements is described in US. Pat. No. 3,453,496 but this circuit relatesprimarily to counter means whereby the number of rockets fired may bepredetermined. An all-electronic intervalometer is shown by US. Pat. No.3,316,451.

Airborne power supplies, particularly those of military aircraft,generally have poor regulation and are susceptible to short periodtransients including millisecond intervals of total power dropout. Suchtransients may totally disrupt operation of an electronic timingarrangement or change its phase. Should such disruption or change inphase occur in an electronic timer during the course of firing of agroup of devices, the result may be an unacceptably lengthened intervalbetween successive firings or, even worse, the failure to fire onerocket of a group whereby the aircraft may continue its operationwithout knowledge by the pilot that he still carries a live round.

SUMMARY OF THE INVENTION The apparatus and method of the inventioncomprise a means and method for maintaining the solenoid of the steppingswitch substantially fully energized throughout substantially the entiretime period while it is subjected to shocks resulting from rocketfiring. The

apparatus and method provide relatively long-duration pulses ofenergizing power to the solenoid, followed by short-duration periods ofsolenoid de-energization. Means are provided to fire the rockets duringsuch periods of solenoid de-energization. The solenoid-energizing pulsesare correlated to the rocket-firing times, and to the shock-transmissiontimes, in such manner as to assure the above-indicated solenoidenergization while shocks are applied to the intervalometer.

The electronic portion of the present electromechanical intervalometerapparatus comprises an astable (free-running) multivibrator oscillatorwhich is asymmetrical or unbalanced. The manner of unbalance is thateach cycle of oscillation has two portions, a long portion and a shortportion, and such portions are caused to be of such durations that thesolenoid motor of the stepping switch is energized during substantiallythe entire time period when major shocks and vibrations are transmittedthereto from the rockets. Since the solenoid is thus energized, it islocked and is rendered immune to the shocks and vibrations. Thresholdmeans are provided in the multivibrator to insure that the transistor onthe long-period side of the multivibrator turns on before the transistoron the short period side, but the threshold means is also caused to besuch that, for this first cycle only, the duration of the pulsegenerated when the long-period side is on will be relatively short. Suchfirst pulse is caused to be sufficiently short that firing occurs only avery short time period after the pilot or commander pushes the startbutton. To avoid disruption of timing in the case of temporary powerdropout, power storage is provided for the multivibrator and a separatepath is provided for negative transients from the solenoid coil that mayoccur upon power dropout. The circuit is extremely rugged and reliableyet characterized by simplicity and by small numbers of components, theresult being that it may be packaged in an extremely small space andthereby meet military requirements for intervalometers having noelectronic components.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a schematic diagram of an electromechanical intervalometerincorporating the present invention;

FIG. 2 shows a wave representing the voltage present at the collector ofthe transistor on the long-period side of the multivibrator oscillator;

FIG. 3 shows a wave representing the base voltage of such transistor;

FIG. 4 shows a wave representing the base voltage of the transistor onthe short-period side of the multivibrator;

FIG. 5 shows a wave representing the collector voltage of thelast-mentioned transistor;

FIG. 6 represents the current pulses through the solenoid motor of thestepping switch, and also represents the positions of the steppingswitch; and

FIG. 7 represents the pulses of firing current delivered to the firingdeck of the stepping switch and thus to the rockets.

The vertical scales of FIGS. 2 through 5 represent voltage, and those ofFIGS. 6 and 7 represent current, but the various voltage scales do notnecessarily correspond to each other, nor do the current scalescorrespond to each other. However, the horizontal time scales correspondso that corresponding portions of the six curves shown in FIGS. 2 7 aredirectly above each other as illustrated by dashed vertical lines.

DESCRIPTION OF A PREFERRED EMBODIMENT:

Throughout this specification, the convention is adopted that acapacitor is charging when its voltage is changing relatively slowly,and is discharging when its voltage is changing rapidly. Forconvenience, the portion of the multivibrator oscillator which containsa transistor which is on for a relatively long period of time is termedthe long-period side of the multivibrator. Conversely, the portion ofthe oscillator containing the transistor which is on for a relativelyshort period of time is termed the short-period side of themultivibrator.

Referring to FIG. 1, the firing deck of a conventional stepping switchor intervalometer is indicated at 10 and may comprise anelectrically-conductive wafer or disc 11 having a lug or ear 12 at oneportion thereof and which forms the movable contact. Such movablecontact 12 is initially not in engagement with any stationary contact,being instead in a safety position. However, the first time the switchsteps the contact 12 is shifted clockwise into engagement with a firststationary contact 13. Similarly, upon each subsequent step of theswitch the contact is shifted clockwise into engagement with subsequentstationary contacts 14 19.

Contacts 13 19 have connected therewith, respectively, rocket igniters20 26. For example, each such igniter may comprise a small-diameter wireadapted to burn (and thus ignite the powder in a rocket) when a currentpulse is passed therethrough between a sta tionary contact (such as 1319) and ground.

It is to be understood that many more stationary contacts are normallyprovided than are here illustrated. For example, there may be nineteencontacts associated with the disc 11, and these contacts may be doubleso that two rockets are fired after each stepping of the wafer l 1.

The stepping switch further comprises a wafer or disc 28 formed ofelectrically conductive material and having a single notch 29 therein.Such wafer is mounted on the same shaft as is the wafer 11 of the firingdeck 10, and therefore rotates therewith and in the same direction(clockwise). A contact 30 is in continuous engagement with theelectrically conductive wafer 28 at all times except when it has rotatedclockwise for almost 360 and the notch 29 becomes registered with thecontact 30. The elements 28 30 insure that the entire apparatus may onlybe operated during one revolution of the wafer 11 of the firing deck 10.

The solenoid-type actuating motor for the stepping switch is indicatedschematically at M, with the solenoid (electromagnet) being illustratedat 31. Motor M may be of the type described in US. Pat. No. 2,496,880,which patent is referred to in the abovecited prior-art US. Pat. Nos.3,384,728 and 3,405,376. Such solenoid motor is so constructed that whenthe winding thereof is energized the armature will be magneticallymaintained clamped or locked close to the winding.

For purposes of the present description, and for no other purpose, theelements described thus far relative to the letter M and to numbers 1031 may (as a matter of convenience, to shorten the presentspecification) be regarded as the same as are described in the citedprior-art US. Pat. Nos. 3,384,728 and 3,405,376 except, however, that nointerrupter switch is employed. Such patents, and also US. Pat. No.2,496,880, are therefore incorporated by reference herein as though setforth in full.

The characteristics of the mechanisms described in the patents cited inthe preceding paragraph are such that the wafer (and also wafer 28)shift through one step each tine solenoid 31 is energized. However, suchwafers do not step (but instead remain stationary) upon eachde-energization of solenoid 31. The wafers remain stationary, when thesolenoid is de-energized, despite the fact that after eachdeenergization of solenoid 31 a return spring shifts the armature backto a new position setting up the mechanism for an additional powerstroke. Such operation is accomplished by ratchet or equivalent means.

For convenience, in the present specification and claims, the entirecombination of the deck 10 and the solenoid-type rotary stepping motor Mare sometimes denoted the stepping switch. Also, the wafers andassociated contacts are sometimes termed the stepping switch or therotary switch. Such interchangeability of nomenclature is occasioned bythe fact that the switch disc 11, wafer 28 and motor M are normally (butnot necessarily) incorporated in a single mechanism in the same smallspace. The term solenoid is not intended to imply a limitation (forexample, to the type of construction where the armature extends into thecoil), but instead encompasses all forms of electromagnetic windings andassociated armatures.

A.D.C. power source is schematically represented at 32, the positiveside of such source being connected through a push-button start switch33 to contact 30. Such start switch 33 is in the pilots compartment ofan airplane, or is operated by a commander on the ground. The disc orwafer '28 is electrically connected to a positive lead 34 'so that suchlead may have a nominal voltage of, for example, 28 volts. It is to beunderstood, however, that this voltage actually varies relativelywidely, as indicated above. The negative side of power source 32 isconnected to a negative lead 36 which is grounded.

In order to eliminate the effects of the voltage fluctuations, thenegative lead 36 is connected to the anode of a zener diode 37. Thecathode of such diode is connected to a regilated-voltage lead 38 which,in turn, is connected through a biasing resistor 39 and an isolatingdiode 75 to the unregulated positive lead 34. The relationships are, inthe present specific example, caused to be such that the voltage of theregulated-voltage lead 38 is plus 7 volts. As in all examples andillustrations stated in this patent application, the values are onlyspecified by way of illustration and are not to be regarded aslimitations.

THE ASTABLE, ASYMMETRICAL MU LTIVIBRATOR OSCILLATOR collector oftransistor 41 to a collector resistor 44 and thence via diode 75 to theunregulated (nominal 28 volts) positive lead 34. A lead 46 connects thecollector of transistor 42 to a collector resistor .47 and thence to theregulated (7 volts) positive lead 38. The base of transistor 41 isconnected through a timing resistor 48 to regulated lead 38, whereas thebase of transistor 42 is connected through a timing resistor 49 to suchregulated lead.

The emitter of transistor 41 is connected to the base of an NPN powertransistor 51 whereas the collector of such power transistor 51 isconnected to the solenoid 31 and thence directly to unregulated lead 34.The emitter of transistor 51 is connected to ground.

The emitter of transistor 42 is connected. to a threshold means andthence to ground lead 36. The illustrated threshold means comprises twodiodes 52 and 53 (a double diode).

A capacitor 54 is connected between the collector of transistor 42 andground lead 36, and serves the purpose of insuring against cessation ofoscillations despite extremely short interruptions in the power supplyfrom source 32 as will be more particularly described below. The size ofcapacitor 54 is sufficiently small to prevent substantial interferencewith the multivibrator operation, but sufficiently large to insurecontinuity of operation despite momentary (micro-second or less) powerlapses.

A capacitor 56 is provided in a lead 57 which extends between lead 43(at a point between collector resistor 44 and the collector oftransistor 41) and the base of transistor 42 (that is to say, the leadwhich extends from such base to resistor 49). Correspondingly, acapacitor 58 is connected in a lead 59 which extends between lead 46 (ata point between the collector of transistor 42 and the collectorresistor 47) and the base of transistor 41 (that is to say, the leadwhich extends between such base and resistor 48).

The threshold means 52-53 plays an important part in the transientoperation of the circuit, occurring immediately after pressing of thestart button 33. This is described in detail below. The transistor 51 isan output means related to the solenoid 31 and thus to other elementswhich respond to the multivibrator (and also to the opening transient)operation. I

There will next be described the normal or steadystate multivibratoroperation of the multivibrator oscillator (this to be distinguished fromthe beginning or transient operation thereof).

In the exemplary form of the present circuit, capacitor 56 has a valuewhich is the same as that of capacitor 58. According y, and since themultivibrator is to be asymmetrical or unbalanced, the value of timingresistor 48 is caused to be smaller than that of timing resistor 49. Theresistor 48 and capacitor 58 combine to form the time constant fortransistor 41 on the longperiod side of the multivibrator.Correspondingly, resistor 49 and capacitor 56 combine to form the timeconstant for transistor 42 on the short-period side. It is to be notedthat the relative lengths of the turn-on times of transistors 41 and 42are not determined solely by such time constants, this being because oneside of the multivibrator is connected to the 7-volt lead 38, whereasthe other side is connected to the 28-volt lead 34. As stated below,however, the voltage supplied by the 28-volt lead is clipped by atransistor which clamps the voltage of lead 43 to a value onlyapproximately 1 volt above the 7-volt voltage of regulated lead 38 (whentransistor 41 is in off condition).

Let it be assumed that, at a particular instant in the steady-stateoperation, the base voltage of transistor 42 is at point A indicated inFIG. 4. At this particular instant of time, the base voltage oftransistor 42 has just been pulled down (due to turn-on of transistor41), so that transistor 42 is turned off. Stated otherwise, the turn-onof transistor 41 connects the collector of such transistor to ground viatransistor 51, causing the collector voltage of transistor 41 to drop toonly one diode drop (the base-emitter junction of transistor 51) aboveground. This negative voltage step is transmitted through lead 57 andcapacitor 56 to the base of transistor 42, thoroughly turning off thelatter.

At this same time (point A in FIG. 4), the voltage at the collector oftransistor 42 is starting to rise exponentially (as shown in FIG. towardthe plus seven voltage of lead 38. The rise in exponential becausecurrent through resistor 47 is now diverted (due to turn-off oftransistor 42) through capacitor 58 to transistor 41 and thence toground lead 36. Also, some current flows through resistor 47 tocapacitor 54 and thence to ground.

Also at this instant of time, point A, current is flowing throughcapacitor 56, namely, through a circuit which starts a plus lead 38 andcontinues through resistor 49, lead 57, capacitor 56, transistor 41,transistor 51 and ground lead 36. Current flow through such circuitproduces a relatively slowly varying change in the voltage of capacitor56, and is therefore (in accordance with the convention stated at thebeginning of this specification) referred to as a charging current. Suchcharging current effects charging of capacitor 56 as indicated in FIG. 4(the base of transistor 42 being directly connected to such capacitor).

At the end of the period A-B (FIG. 4) which is the charging period forcapacitor 56, as stated above, the base of transistor 42 rises toturn-on voltage and causes such transistor 42 to commence to turn on.Referring to FIG. 5, such initiation of turn-on of transistor 42 causethe voltage of the collector of such transistor to commence a negativetransition (the collector voltage dropping in response to initiation ofcurrent flow through transistor 42, due to the presence of resistor 47).The resulting negative rate of change of voltage at the collector oftransistor 42, and thus in the connected capacitor 58, results in acurrent flow through such capacitor 58. The rate of change at thecollector of transistor 42 being negative, the current flow throughcapacitor 58 is from left to right and causes draining of the currentwhich previously passed from lead 38 through resistor 48 to the base oftransistor 41.

The base current of transistor 41 is therefore diverted, and (when therate of change of voltage at the collector of transistor 42 becomessufficiently high) a sufficient amount of base current is diverted fromtransistor 41 to cause such transistor 41 to go out of saturation. Atthat time, the collector voltage of transistor 41 commences to rise,thereby resulting in a discharging current through lead 57 and capacitor56 (left to right) to reinforce the base current of transistor 42 andcause the latter to turn on fully. Transistor 41 thus turns ofi rapidly,and transistor 42 turns on rapidly, all in a matter of microseconds orless.

The preceding description thus covers the time period between points Band C, FIG. 4, point C being the point where transistor 42 is saturatedand transistor 41 is fully turned off.

After point C in FIG. 4, capacitor 56 continues to discharge. Thedischarge circuit may be traced from lead 34 through resistor 44, lead43, lead 57, capacitor 56, transistor 42 and ground lead 36. At the sametime, capacitor 58 is charging due to current flow from plus lead 38through resistor 48, lead 59, capacitor 58, transistor 42 and ground.The charging of capacitor 58 is indicated in FIG. 3 since capacitor 58is directly connected to the base of transistor 41. At point D, the basevoltage of transistor 41 has risen to the point where such transistorstarts to turn on.

As described above relative to transistor 42, the initiation of tum-onof transistor 41 creates a negative rate of change of voltage at thecollector of such transistor 41, resulting in current flow from lead 38through resistor 49 and capacitor 56 to transistor 41 and thence totransistor 51 and ground. This diverts base current from transistor 42and causes the latter transistor to come out of saturation. Thereupon,the collector voltage of transistor 42 starts to rise, causing currentto flow through capacitor 58 and to the base of transistor 41, turningsuch latter transistor on hard. The collector voltage of transistor 41therefore drops to a small amount above ground voltage, as shown in FIG.2, thereby resulting in transmission of a negative step voltage throughcapacitor 56 to the base of transistor 42, thoroughly turning off thelatter transistor. The initial point A of the cycle (FIG. 4) istherefore reached.

OUTPUT ELEMENTS WI-IICH RELATE THE- MULTIVIBRATOR TO THE STEPPING SWITCHOne of the main elements which relate the multivibrator to the steppingswitch (including the firing deck 10) is the above-indicated powertransistor 51, and which forms a first output means. Such transistor isconnected in a lead 60 which extends from the unregulated positivevoltage line 34 to ground lead 36 via solenoid 31. The solenoid istherefore energized throughout the time period when the transistor 51 ison, the solenoid current being indicated in FIG. 6. Transistor 51 is onat all times when multivibrator transistor 41 is on, since the emittercurrent of the latter transistor is transmitted through the base ofpower transistor 51.

Two additional transistors are provided to associate the multivibratorwith the stepping switch, namely, transistors 61 and 62 which form asecond output means. Transistor 61 is an NPN transistor the base ofwhich is connected to lead 43 (between resistor 44 and transistor 41)and the emitter of which is connected to regulated lead 38. Thecollector of transistor 61 is connected to a lead 63 which extends tothe base of transistor 62, the latter being a PNP power transistor. Theemitter of transistor 62 is connected to the unregulated positive lead34, whereas the collector thereof is connected to the wafer 11.

Each time when transistor 41 saturates, during the above-describedmultivibrator operation, the voltage of the lower end of resistor 44 ispulled down to a low voltage near ground. As soon as transistor 41 turnsoff,

during the multivibrator cycle, the collector voltage of such transistortries to fly up to the plus 28 voltage of lead 34. However, such voltageof lead 43 (collector of transistor 41) never reaches 28 volts becauseit is clipped by operation of the base-emitter junction of transistor61. The base of transistor 61 is thus clamped (when transistor 41 isoff) at a value above that of the 7-volt lead 38.

When transistor 41 turns off, the current which previously passedtherethrough from lead 34 via resistor 44 passes instead to the base oftransistor 61, thence through the emitter of such transistor to lead 38and down through zener diode 37 to ground. This effects turn-on of ,thetransistor 61 and, accordingly, effects turn-on of power transistor 62(because the base of the latter transistor is in the collector circuitof transistor 61). Tum-on of power transistor 62 completes a firingcircuit through which firing current (FIG. 7) is supplied from plus lead34 to wafer 11 and thus to the rocket igniters 20-26.

It will thus be seen that transistor 51 constitutes a first electronicswitching means controlled by the multivibrator, and that transistors 61and 62 constitute second electronic switching means controlled thereby.

I IMPORTANT TIMING AND DUTY CYCLE RELATIONSHIPS As indicated above,current is supplied to the firing deck when transistor 41 of themultivibrator is off, whereas, conversely, current is supplied to thesolenoid 31 when the same transistor 41 is on. The current throughsolenoid 31, and the deck current through transistor 62, are thereforeout of phase relative to each other as shown in FIGS. 6 and 7. The deckcurrent may be referred to as firing pulses (FIG. 7), whereas the pulsesthrough the solenoid 31 may be referred to as holding pulses (FIG. 6)since these pulses cause the armature of the solenoid motor M to be helddown and thereby effectively resist the effects of shock.

Thus, in accordance with the apparatus and method of the presentinvention, each firing pulse is delivered during a time when there is nosolenoid current, and thus no holding of the armature in its retractedcondition. Also in accordance with the present invention, a holdingpulse is supplied to the solenoid sufficiently soon after each firingpulse that the armature of the solenoid-operated stepping motor isshifted to retracted condition before the shock wave resulting from thefiring pulse is received by the intervalometer. Stated otherwise, therelationships between the firing pulses and the holding pulses arecaused to be such that the delay which occurs after each firing pulse(FIG. 7), and prior to the time the shock reaches the intervalometer, issufficiently long that no substantial shock is felt before the nextsolenoid pulse is delivered to thereby shift the armature to retractedposition.

The intervalometer is normally mounted in a recess adjacent the outersurface of a pod containing numerous rockets. When a firing pulse isreceived by one of the igniters (such as -26) in the pod, a certainamount of time is required for the igniter to burn and thereforecommence ignition of the rocket. In addition, a certain amount of timeis required for burning of the powder in the rocket. Furthermore, timeis required for transmission of the shock wave through the pod to theintervalometer. In accordance with the present method and apparatus, thetime interval between each firing pulse and each holding pulse is causedto beshorter than the elapsed time resulting from all of the factorsenumerated in the present paragraph, the result being that the armatureis effectively restrained (solenoid current on) by the time the shockwave is felt.

in accordance with another major aspect of the present method andapparatus, the solenoid pulse is not only supplied sufficiently soonafter firing to insure that the armature will be restrained before theshock wave is felt, but each solenoid pulse (after the first one, asstated under the following subheading) is caused to be sufficiently longto insure that all substantial shocks and vibrations will dissipatebefore the application of the power to the solenoid is discontinued.Thus, the duty cycle of the solenoid is caused to be high, much higherthan in prior-art apparatus and methods. The duty cycle of the solenoid31 is at least 50 percent and should be much higher. Preferably, theduty cycle is in the range of 60 percent to 90 percent. An exemplaryduty cycle for the solenoid 31 is on the order of 75 percent. Thedesired duty cycle is achieved by varying the above-indicated timeconstants, and applied voltages, in the multivibrator.

The specified duty cycles relate to the time when power is applied tothe solenoid 31 as compared to the time when the supply of power to thesolenoid 31 is discontinued. Thus, the duty cycle illustrated in FIG. 6is approximately percent.

Stated in another manner, the aggregate time that power is applied tothe solenoid 31 is equal to or greater than, and is preferably severaltimes greater than, the aggregate time that no power is applied thereto.Thus, the solenoid 31 is substantially fully energized the majority ofthe time during each cycle of operation.

In summary, therefore, the holding pulses are delivered to solenoid 31sufficiently soon after rocket ignition, and are caused to besufficiently long, that substantially all shock is dissipated while thearmature is magnetically restrained. The armature is only permitted tomove during intervals when there is no substantial shock, so that theentire intervalometer is under predetermined electrical control and issubstantially immune to shock effects. For similar reasons, the adverseeffects of extreme temperatures, and other environmental conditions, arerendered unimportant.

TRANSIENT CONDITIONS FOLLOWING PRESSING OF START BUTTON 33 There willnext be discussed the conditions which occur immediately followingpressing of the button 33 by the pilot or field commander. It iscritically important that the first rocket fire a very short timeinterval following pressing of such button, it being unsatisfactory todelay for a time period represented, for example, by one of the longpulses shown at the right side of the wave shown in FIG. 5.

In accordance with a major aspect of the present invention, theabove-indicated threshold means, for example the two diodes 52 and 53,are provided in order to achieve two important results, namely:

a. Making sure that multivibrator operation always starts with turn-onof the transistor 41 on the longperiod side instead of the transistor 42on the shortperiod side, and

b. Causing the first pulse generated by the longperiod side to beabbreviated, as shown at the left end of FIG. 5.

It is pointed out that the base of transistor 41 on the long-period sideof the multivibrator is two diode drops above ground, namely, thebase-emitter junction of transistor 41 and the base-emitter junction oftransistor 51. Because of the presence of the two diodes 52 and 53, thebase of transistor 42 is initially three diode drops above ground,namely, the base-emitter junction of transistor 42 and the double diode52-53. This additional diode drop between the base of transistor 42 andground is what insures that the transistor 41 will be the first to fireupon pressing of start button 33. Furthermore, and very importantly, thenumber of diode drops between the base of transistor 42 and ground is socorrelated to other parameters in the circuit that transistor 42 willturn on a relatively short period of time after turning on of transistor41, so that the first pulse generated by the long-period side of themultivibrator will be abbreviated. I

Prior to pressing of start button 33, all of the capacitors 56, 58 and54 are fully discharged. Upon pressing of start button 33 by the pilot,the unregulated positive lead 34 comes up to its 28-volt voltage withina fraction of a microsecond. It may be noted parenthetically at thispoint that a storage capacitor 76, the function which will be describedin detail below, is coupled between ground and the diode 75. Capacitor76 has no appreciable effect upon the rise time of voltage onunregulated positive lead 34 since the resistance between this capacitorand the power source 32 is very small. However, the node or junctionpoint 66 (junction between leads 59 and 46) in the multivibrator remainsat zero volts instantaneously. Since the base of transistor 41 isconnected to such node 66 through capacitor 58, such base of transistor41 also remains at zero volts instantaneously. Because, at the verybeginning of operation following pressing of button 33, the base oftransistor 41 is thus at zero volts, such transistor 41 is in offcondition.

After start button 33 is pressed, both sides of capacitor 56 start torise rapidly toward the 28-volt voltage of line 34. The voltage rise onthe right side of capacitor 56 causes the base-collector (not thebase-emitter) junction of transistor 42 to become forward biased,whereupon such base-collector junction starts to conduct.

A path for flow of substantial current is thus created from theunregulated lead or line 34 through diode 75, resistor 44, capacitor 56,the base-collector junction of transistor 42, capacitor 54 and ground.In addition, there is a substantial current flow from line 34 throughdiode 75, the relatively small resistor 39, the relatively smallresistor 47, capacitor 54 to ground. There is an additional smallcurrent flow, namely, one from lead 34 through diode 75, resistor 39 andthe large resistor 49 to the base-collector junction of transistor 42and thence through capacitor 54 to ground, but this latter flow is sosmall in comparison to the others that it may be disregarded.

The above-described current rapidly charge capacitor 54, causing thevoltage at the collector of transistor 42, and also at the connectednode 66, to rise rapidly. Such rapid rise is transmitted throughcapacitor 58 to the base of transistor 41. This causes turn-on oftransistor 41 and thus of the associated power transistor 51, so thatsolenoid 31 becomes energized as shown at the left end of FIG. 6.

It is important to note that the two diodes 52 and 53 prevent transistor42 from turning on at this time, there being insufficient voltage at thebase of such transistor to overcome the three diode drops indicatedabove. Thus, it is only the base-collector junction of transistor 42which goes into conduction.

All of the above occurs in a very short time period, for example 541)microseconds.

The described turn-on of transistor 41 assimilates or draws totransistor 41 current which previously flowed through thefirst-mentioned one of the above-indicated paths (through resistor 44,capacitor 56, and the basecollector junction of transistor 42), causingsuch basecollector junction of transistor 42 to cease conduction. Thecurrent which previously flowed in the secondmentioned one of theabove-indicated paths (through resistor 47) now passes into capacitor 58as well as into capacitor 54. Such current flow from line 38 throughresistor 47 and capacitor 58 to the base of transistor 41 causes thelatter transistor to turn on hard, and such transistor goes intosaturation. Accordingly, the collector voltage of transistor 41 drops bya predetermined amount down to only one diode drop (the base-emitterjunction of transistor 51) above ground. Such predetermined drop in thevoltage at the collector of transistor 41 is felt (through capacitor 56)by the base of transistor 42, and causes multivibrator operation tostart with a predetermined desired charge on capacitor 56.

As multivibrator operation thus commences, the base voltage oftransistor 42 (charge on capacitor 56) is approximately at point E shownat the extreme left end of FIG. 4. It will be noted that such point E isat a much higher voltage level than is the point A which was describedabove relative to the normal or steady-state operation of themultivibrator, which means that the time period elapsing between point Band point F (when transistor 42 turns on due to a sufficient amount ofcharging of capacitor 58 via a circuit from line 38 through resistor 47)is much shorter than the time period elapsing between point A and pointB.

Because of the selection of the proper threshold means between theemitter of transistor 42 and ground, and also because of the use ofcapacitors having the necessary values, the time which elapses betweenpoint E and point F of FIG. 4 is approximately equal to the timerequired to effect initial stepping of the solenoidoperated steppingmotor M. Stated otherwise, the duration of the resulting solenoidcurrent pulse (shown at the extreme left of PEG. 6) is sufficientlygreat to cause the solenoid switch or deck to step to its firstposition.

if there were three diodes between transistor 42 and ground, instead oftwo, the portion E-Fof the curve of FIG. 4 would be much longer, and thedelay between pressing of button 33 and the first firing pulse to thefiring deck MD would be longer. It is only desired to cause the firstpulse of solenoid current to be sufficiently long to insure that theswitch deck is shifted from safety position to its first firing position(ear 12 resting on the first stationary contact 13), so that immediatelythereafter a current pulse may be transmitted through the deck to firethe first rocket. The short-pulse operation thus causes firing of thefirst rocket a short time after start button 33 is pressed.

Although the above description has been given relative to a circuitincluding capacitor 54, it is emphasized that such capacitor 54 is notessential to this initial tum-on operation. Instead, as previouslystated, such capacitor is primarily intended to maintain themultivibrato'r in operation despite short lapses in the power suppliedfrom source 32. Nevertheless, in the presence of some transients orunsteadiness in the power supply, capacitor 54 does assist the steeringdiodes 52, 53 in ensuring that transistor 41 is the one that turns onfirst.

If there were no capacitor 54, the above-described initial transientoperation would be substantially the same except there would be noSO-microsecond delay. Current through the base-collector junction oftransistor 42 would then pass through capacitor 58 to the base oftransistor 41. There being nothing to ground the node 66, the voltage atsuch node would fly up instantaneously upon pressing of button 33.

SUMMARY OF INTERVALOMETER OPERATION There will next be set forth a briefsummary of the ripple or intervalometer operation, this beingdistinguished from the single-shot operation described under the nextsubheading.

Prior to the time the pilot or field commander presses the start button33, all of the elements are in the positions shown in FIG. 1. The ear 12of the wafer 11 on firing deck is therefore not engaged with any of thestationary contacts 13-19, being instead in safety position. Uponpressing of button 33, and as described in detail in the previoussubheading, the transistor 41 on the long-period side of themultivibrator is the first to turn on. Such tum-on of transistor 41causes turn-on of transistor 51 and consequent energization of solenoid31 of the stepping switch, as shown by the left pulse in FIG. 6. Also asstated under the previous subheading, the solenoid current flows for atime period barely sufficient to cause the firing wafer 11 to step toits first firing position, car 12 then being engaged with the firststationary contact 13. Such first firing position is represented by thenumeral 1 in FIG. 6.

As soon as transistor 41 turns ofi and transistor 42 turns on, as aresult of the above-described multivibrator operation, the voltage inlead 43 flies up until transistor 61 turns on, with consequent tum-on oftransistor 62 to deliver a firing pulse from the unregulated lead 34through transistor 62 and through the deck 10 to the contact 13 andthence to the first rocket igniter and ground. The first rocket thusfires during a time when the solenoid 31 is de-energized. Although thesolenoid is de-energized, there is no motion of the deck since, asstated above, the mechanical elements in the stepping switch are suchthat stepping only occurs upon energization of the solenoid and not upondeenergization thereof. Thus, as shown by the leftmost arrow in FIG. 6,the switch remains in its first firing position.

The firing of the first rocket (or pair of rockets) creates the verypowerful shock indicated above but, because of the factors previouslystated, such shock does not reach the intervalometer until the solenoid34 is again energized as indicated by the second pulse in FIG. 6 (whichresults from the subsequent turn-on of transistor 41 on the long-periodside of the multivibra: tor) and as a result of the normal multivibratoroperation. It is emphasized that such second pulse transmitted throughthe solenoid and all subsequent solenoid pulses are long. Such pulsesare sufficiently long that the solenoid will be energized throughout theentire period when .substantial shocks and vibratoryforces aretransmitted to the intervalometer. The consequent magnetic clamping downof the armature of the solenoid motor M therefore prevents the erraticfiring which is characteristic of prior-art apparatus.

The second pulse (FIG. 6) transmitted through solenoid 31 not onlyclamped down the armature of the stepping switch motor but also causedstepping of the ear 12 of the firing deck 10 into engagement with thesecond stationary contact 14. This is represented by the numeral 2 inFIG. 6. Accordingly, as soon as transistors 41 and 51 turn off duringnormal multivibrator operation, transistors 61 and 62 turn on to causetransmission of a firing pulse through the abovedescribed circuit to thecontact 14 and thus to the second rocket igniter 21.

The operation then proceeds as described above until the stepping switchhas stepped to all contacts 13-19, and all of the rockets have beenfired. The third and fourth firing positions are indicated by numerals 3and 4 in FIG. 6, and such positions are maintained as indicated by thearrows. The above-described disc 28 having notch 29 therein insures thatthere will be no recycling despite any continued pressing of the button33.

'All of the rockets are thus fired (a firing sequence or ripple) in avery short period, such as 600 milliseconds (it being remembered thatthere are normally more contacts than are shown in the illustrated deck10). The ripple time may be varied, for example to 400 milliseconds, byadjusting the time constants in the multivibrator. In a typicalintervalometer incorporating the present invention, each cycle mayrequire milliseconds, during which the solenoid current is on for about45 milliseconds. In another application, each cycle requires 40milliseconds, during which the solenoid current is on for 25milliseconds.

The rockets fire in such manner, without erratic operation, that thereare no aerodynamic disturbances, misfiring, excessive spreading, orother adverse characteristics of prior-art apparatus.

SINGLE-SHOT OPERATION All of the above description relates to the rippleor multiple firing of the rockets. This occurs when a ripple switch R,FIG. 1, is in the illustrated position connected to a blind contact.

When single-shot operation is desired, the ripple switch is shifted toits other position in order to permit closing of a circuit which extendsfrom the plus voltage lead 34 through a lead 69 and a current-limitingresistor 71 to the junction between the emitter of transistor 41 and thebase of transistor 51.

When the ripple switch R is thus shifted away from the illustratedripple position, the pressing of start switch 33 causes transistor 51 toturn on hard, and thus completes a circuit through solenoid 31. Thefiring deck wafer l 1 therefore immediately steps, causing the ear 12 toengage the first stationary contact 13 (firing position 1 Although thelead 69 from the 28-volt supply lead 34 is also connected to the emitterof transistor 41, there is not much change in the emitter voltage ofsuch transistor since the lead 69 is only one diode drop above ground(the base emitter junction of transistor 51). The multivibratortherefore operates substantially the same as described above, and startswith the short first pulse just as is the case when the switch R is inthe illustrated ripple position. It follows that, as soon as thesolenoid 31 effects stepping of the deck 10, a firing pulse will bedelivered to the deck and thus to the first rocket igniter 20. Thus, therocket fires very shortly after pressing of button 33 as desired.

Since the solenoid remains energized during the entire time that thepilot or field commander maintains his finger on button 33, there willbe no stepping of the switch while such button is maintained pressed.Subsequent firing pulses may be delivered to the rocket igniter 20, butthey will be ineffectual since the rocket has already fired.

In order to fire the second rocket, the pilot releases the button 33 andthen presses it again, thus repeating the described cycle.

POWER DROPOUT PROTECTION The airborne power supply is subject to variousirregularities of which two may be classified as (a) very short firingtransients and (b) longer contact dropouts. The very short firingtransients are micro or nanosecond duration transients, largely due torocket firing. To enhance reliability, the pulse to the rocket firingsquib is of 15 milliseconds duration although the squib itself requiresonly four milliseconds for complete burnout. When the firing pulse isapplied, it is supplied as a 4 ampere pulse through a 5 ohm resistor tothereby create a volt drop in the voltage on the power line as seen atthe input to the intervalometer. This is an exceedingly sharply risingwave front of the indicated short duration. Nevertheless, it may besutficiently long and sufficiently large to toggle the multivibrator ata point in its cycle that is not in phase with its normal toggling(changing of state). This short but sharp wave front is a voltagefunction that also occurs when buming of the firing squib has beencompleted. At such time the voltage on the power line rapidly returns toits 28 volt nominal level and again the circuit is subjected to a sharp,short transient which may toggle the multivibrator out of phase.

Capacitor 54 is sufficiently large to eliminate the adverse effects ofthese very sharp transients. By preventing such sharp changes in thecollector of transistor 42, both sides of the multivibrator areeffectively protected against these transients. Capacitor 54, connectedbetween the collector of transistor 42 and ground, also helps to steerthe tum-on to the long side of the multivibrator, transistor 41 in thepresence of unsteady power supply as described above. The additionalfunction of capacitor 54 is to prevent relatively fast firing transients(on the order of microseconds or even nanoseconds) from commutating ortoggling the multivibrator.

Other transients occur in the power supply such as the contact dropoutsreferred to above. These are due to faulty wiring connections betweenthe power supply and the intervalometer. The latter is normallypositioned in or about the rocket launching mechanism, carried in a podor other structure externally of the aircraft. In the usual arrangement,in addition to the pilots firing button, there are many switches, wiringconnectors, plugs, safety devices, and the like, interposed in theelectrical line between the power supply and the intervalometer. Thesedevices are all subject to chattering or intermittent contact. Inparticular, as the structure and circuitry become older and have beensubjected to the harsh and continuously vibrating environment of aflying aircraft, the various connections become loose, worn and frayed.Thus, it is common in a conventional aircraft to accept a power supplythat is frequently subjected to partial power dropouts having a durationof as much as l millisecond.

Such power dropouts may have serious adverse effects upon circuitoperation. They may result in completion of a full ripple firing cyclein which the interval between a pair of successive rocket firings hasbeen unacceptably enlarged. Consider for example, an instant of timethat follows by 2 milliseconds the initiation of a rocket firing pulse.Assume that at such instant there is a l millisecond, more or less,power dropout. Note that the rocket squib has not yet fired since thelatter requires approximately 4 milliseconds to complete its burn. Thefiring pulse is applied for 15 milliseconds to ensure the full 4millisecond squib burnout. It is possible that during and because of the1 millisecond power dropout, the multivibrator will be toggled (changestate). Thus, when the power comes back on after the 1 milliseconddropout, a holding pulse would be applied to the solenoid coil, thefiring deck would switch to the next firing squib, and that rocket ofwhich the firing squib was receiving a firing pulse at the time ofdropout would remain unfired. In such a situation, it is entirelypossible that the aircraft would return to its base or continue itsoperation without the knowledge by the pilot that he was carrying alive, unfired rocket.

Again consider a 1 millisecond, more or less, power dropout that occursshortly after the holding pulse is supplied to the solenoid coil, butbefore the solenoid armature had been fully actuated and locked. If uponsubsequent power return, the multivibrator had been toggled, anadditional time would be required before the multivibrator returned tothat point in its cycle at which the firing deck 11 would step to thenext rocket. Thus, the interval between rocket firings has been enlargedby 'a time significantly greater than the duration of the firing pulse.An intervalometer exhibiting firing intervals greater than specifiedamounts is not considered to be acceptable to the militaryorganizations.

The aborting of the solenoid operation upon power dropout may be due inpart to the back electric motive force developed by the solenoid. Thus,upon temporary power dropout, this back EMF could discharge the solenoidso that upon return of power, application of the holding pulse might notbe of sufficient remaining 7 duration to ensure a full throw and lockingof the armature.

In order to eliminate the adverse effects of such relatively longerpower line dropouts, the unregulated power supply line 34 is connectedvia diode 75 to provide ,power to the multivibrator. The multivibratorpower is supplied from diode 75 via resistor 44 to the collector oftransistor 41 and via resistor 39, regulated voltagelead 38 andresistors 47 and 49 to transistor 42.

Also connected to diode 75 is a capacitor 76 having its other sideconnected to ground. Capacitor 76 is a large capacitor, on the order offifteen microfarads or more, having a size limited only by availablephysical space. Capacitor 76 is charged to the nominal 28 volts duringnormal operation by current flowing from switch deck 28 and throughdiode 75. In the event of dropout of power on the power line 34, thecharge on capacitor 76 is isolated from the power supply, from thesolenoid coil, and from the power transistor 62 by means of diode 75.Accordingly, the charge on the capacitor 76 cannot be drained by thepower supply nor by the solenoid, nor by power transistor 62, all ofwhich are connected directly to the unregulated power line 34. Thus, thestepping switch and rocket firing may be momentarily disabled during thepower line dropout but capacitor 76 will continue to supply power to themultivibrator. Accordingly, the multivibrator will remain in phase andits timing will be entirely unaffected by such 1 millisecond, more orless, power line dropout.

Where the capacitor 76 and diode 75 are connected as shown, a momentaryloss of power that occurs during the firing pulse, cannot and will notchange the multivibrator phase, and, thus, when power is returned theremainder of the millisecond firing pulse will be applied to the samerocket Squib which will fire just as if no power dropout had occurred.Similarly, if a power dropout had occurred during a holding pulse, uponreturn of power the holding pulse continues to ensure completion of thearmature stroke and locking of the armature in place without any changeof cycling phase of the apparatus.

In a copending application for Intervalometer and Timing Oscillator byCharles E. Everest, Ser. No. 62,948, filed Aug. 11, 1970, and assignedto the assignee of the present application, there is described ananalogous power dropout storage arrangement. However, the power dropoutstorage of said copending application is connected in a different mannerto ensure continued operation of a unijunction transistor oscillator.Such oscillator drives a silicon control rectifier that initiatesenergization of a solenoid coil having a set of self-interruptingcontacts. In the arrangement of the copending application, power dropouteffects are considerably different, particularly because of the use ofthe self-interrupting solenoid coil.

Power loss in a circuit having a coil such as the solenoid coil 31introduces still other problems due to the back EMF generated by aninductance. Thus, upon loss of power, the upper end of the solenoid asillustrated in FIG. 1 may go sharply negative by an amount sufficient totoggle the multivibrator and change its phase. Change of phase of themultivibrator can result in the several problems detailed above.

Such adverse efiect of the coil EMF upon the multivibrator timing mayoccur through a negative current path from the solenoid through powerline 34 through the emitter base junction of transistor 62, and thencefrom the collector to the emitter of transistor 61 to the regulatedvoltage line 38. This path may produce a sharp negative-going voltagestep on line 38 that could be sufiicient to turn ofi transistor 41 if ithappens to be conducting.

In order to eliminate or at least significantly minimize any current inthe above-described path, a diode 77 is connected between the upper endof coil 31 and ground. Diode 77 is poled so as to provide a lowimpedance path to ground for such a negative-going signal that may occurat the upper end of coil 31 upon temporary power loss.

SPECIFIC EXAMPLE As previously stated, the values of resistance,capacitance, etc., are given by way of illustration only and notlimitation. Certain values are placed in FIG. 1 for purposes ofconvenience, because the relative magnitudes of resistors aid the readerin determining what is occurring, particularly during transientconditions.

Each of resistors 39, 44 and 71 has a value of 120 ohms. Resistor 47 hasa value of 56 ohms, whereas resistor 49 has a nominal value of l kilohm.Resistor .48 has a value of 560 ohms.

'Each of capacitors 56 and 58 has a value of 47 microfarads, whereascapacitor 54 has a value of 12 microfarads.

Zener diode 37 is a 1N534l. Diodes 52, 53, and 77 are all type 1N400l.Each of transistors 41 and 42 is a 2N4401, whereas transistor 51 is aTIP35. Transistor.

61 is an MJE340, whereas transistor 62 is a TIP32.

It is to be understood that the appended claims are to be interpreted asapplying to equivalent circuits wherein complementary transistors areemployed, since the transistors 41 and 42 could readily be replaced byPNP transistors. In the latter event, the diodes 52 and 53 would bereversed so that the anodes thereof would be adjacent ground lead 36 andthe cathodes adjacent the PNP transistor which replaces transistor 42.It is also to be understood that phase inversion may be employedrelative to the various outputs, such as the first and second outputmeans specified above, without avoiding the appended claims. Means maybe provided to discontinue the ripple at any point in the firing cycle,so that not all of the rockets in the bank need be fired after the pilotor ground commander pushes the start button 33. The power transistors 51and 62 may be replaced by thyristors.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims.

We claim:

1. An intervalometer for supplying firing pulses in timed relationshipto a bank of rockets or the like,

which comprises:

a stepping switch operated by a solenoid, means to apply actuating powerto said solenoid at predetermined intervals, said stepping switchstepping from one station to the next upon each of said powerapplications to said solenoid, and

means associated with said stepping switch to supply firing current todifferent rockets in the rocket bank connected to said stepping switch,thus firing such rockets and generating shock forces that are applied tosaid intervalometer during a predetermined period following such firing,

said means for applying power to said solenoid including timing meanscorrelated to the firing times and firing characteristics of saidrockets, and also to the distance between said rockets and saidsolenoid, for maintaining said solenoid in energized conditionthroughout said predetermined period when the shocks and vibrationsincident to the firings of said rockets are applied to said solenoid,whereby to prevent erratic firings of said rockets.

2. The invention as claimed in claim 1, in which said means to supplyfiring current to said rockets includes means for supplying such firingcurrent during periods when there is no power applied to said solenoid.

3. The invention as claimed in claim 2, in which said means to applysaid power to said solenoid includes means for applying such powersufficiently soon after said supplying of firing current to said rocketsthat said solenoid is substantially fully energized when said shocks andvibrations reach said solenoid, and in which said means to apply saidpower to said solenoid includes means for applying the same for timeperiods sufficiently long to maintain said solenoid substantially fullyenergized until said shocks and vibrations are dissipated.

4. The invention as claimed in claim 45 including unidirectional meansfor isolating said storage means from said solenoid and from said rocketfiring current.

5. The invention as claimed in claim 1, in which said means to applypower to said solenoid for predetermined time periods and atpredetermined intervals includes means for energizing said solenoid witha duty cycle of at least 50 percent.

6. The invention as claimed in claim 5, in which said duty cycie is inthe range of 60 to 90 percent.

7. The invention as claimed in claim 1, in which said means to applypower to said solenoid includes means for effecting application of suchpower thereto for an aggregate time longer than the aggregate timeduring which application of such power is discontinued, during eachfiring sequence of the intervalometer.

8. The invention as claimed in claim 7, in which said aggregate timeduring which such power is applied to said solenoid is at least severaltimes longer than said aggregate time during which application of suchpower is discontinued.

9. The invention as claimed in claim 1, in which said means to applypower to said solenoid includes means for maintaining the samesubstantially fully energized for a first period of time, means fordiscontinuing application of power to said solenoid for a second periodof time shorter than said first period of time, means for applying powerto said solenoid for said first period of time, means for discontinuingapplication of power to said solenoid for said second period of timeshorter than said first period of time, and means for repeating saidlong-short relationship until completion of firing of said bank ofrockets.

10. The invention as claimed in claim 9, in which said second period oftime has a duration which is much smaller than said first period oftime.

11. The invention as claimed in claim 1, in which said means to applypower to said solenoid includes means for applying thereto a first pulseof current which is relatively short but still sufficiently long toeffect retraction of the armature of said solenoid, means for thereafterdiscontinuing application of power to said solenoid for a relativelyshort time period, means for thereafter applying to said solenoid asecond pulse of current which is much longer than said first pulse,means for thereafter discontinuing application of power to said solenoidfor said relatively short time period, means for thereafter applying tosaid solenoid a third pulse of current which is much longer than saidfirst pulse, and means for thereafter continuing to supply relativelylong pulses of current followed by relatively short periods ofdiscontinuation of applica tion of power to said solenoid.

12. The invention as claimed in claim 11, in which said means to supply,firing current to said rockets includes means for supplying such firingcurrent during periods when there is no power applied to said solenoid.

13. The invention as claimed in claim 1, in which said means to supplyfiring current to said rockets is a source of current pulses includingelectronic switching means external to said stepping switch.

14. An intervalometer for supplying firing pulses in timed relationshipto a bank of rockets or the like, which comprises:

a stepping switch having numerous stationary contacts adapted to beengaged sequentially by a movable contact, each of said stationarycontacts being connected to the firing means for at least one rocket insaid bank thereof, said movable contact being initially in a safetyposition out of engagement with any of said stationary contacts,solenoid motor mechanism connected to said stepping switch and sorelated thereto that the first energization of the solenoid in saidmechanism effects shifting of said movable contact from said safetyposition to a first position in engagement with the first of saidstationary contacts; the second energization of said solenoid effectsshifting of said movable contact from said first position into a secondposition in engagement with the second of said stationary contacts, andsubsequent energizations of said solenoid efiect successive shifting ofsaid movable contact into successive positions in engagement with othersof said stationary contacts, and means associated with said steppingswitch and with said solenoid motor mechanism to first supply to saidsolenoid a first current pulse sufficiently long to shift said movablecontact from said safety position to said first position, to then sendfiring current through said then-engaged movable contact and firststationary contact, to then supply to said solenoid a second currentpulse sufficiently long to shift said movable contact to said secondposition and also sufficiently long to maintain said solenoidsubstantially fully energized throughout the time when the shocks andvibrations incident to firing of the rocket connected to said fuststationary contact are received by said stepping switch and by saidmechanism, to thensend firing current through said then-engaged movablecontact and second stationary contact, and to then repeat in alternationall of such steps of supplying current pulses to said solenoid andsending firing current through the engaged contacts, excepting thefirstmentioned step of shifting said movable contact from said safetyposition to said first position, whereby the rocket in said bank arefired sequentially in a non-erratic manner.

15. The invention as claimed in claim 14, in which said last-named meanseffects discontinuation of application of power to said solenoid for asubstantial time period after the end of each of said current pulsesthereto, during which time period said firing current is suppliedthrough the then-engaged contacts.

16. The invention as claimed in claim 15, in which said last-named meansis so constructed that the duration of each of said second andsubsequent pulses of current to said solenoid is'substantially longerthan the duration of the period during which application of power tosaid solenoid is discontinued.

17. The invention as claimed in claim 16, in which said means to applysaid pulses to said solenoid includes,

an electrical power supply,

a timing circuit energized from said power supply for applying saidpulses for the aforesaid periods, and

storage means responsive to said power supply for receiving and storingelectrical energy therefrom and for supplying such stored energy to saidtiming circuit to maintain the energization thereof during periods ofloss of power from said power supply.

18. The invention as claimed in claim 16, in which the duration of eachof said second and subsequent pulses is on the order of several timeslonger than the duration of each period of discontinuation ofapplication of power to said solenoid.

19. The invention as claimed in claim 14, in which said last-named meanseffects discontinuation of said first current pulse to said solenoid arelatively short time period after commencement thereof, said short timeperiod being barely sufficient to insure stepping of said movablecontact from said safety position to said first position, said shorttime period having a duration much shorter than that of said second andsubsequent current pulses to said solenoid.

20. The invention as claimed in claim 14, in which said last-named meanssupplies said current pulses to said solenoid sufficiently soon aftersending of said firing current to insure that said solenoid issubstantially fully energized when said shocks and vibrations reach saidsolenoid, and in which said last-named means delivers said currentpulses to said solenoid throughout time periods sufficiently long toinsure that said shocks and vibrations are dissipated before saidsolenoid is deenergized.

21. The invention as claimed in claim 14, in which said last-named meansis an electronic circuit incorporating electronic switching means tosupply said current pulses to said solenoid, and also incorporatingelectronic switching means to supply firing current to said rocket bankthrough the engaged contacts of said stepping switch, saidfirst-mentioned and second-mentioned electronic switching meansoperating in altemation to supply said current pulses to said solenoidand tosupply said firing current to said rocket bank.

22. The invention as claimed in claim 14, in which Said last-named meansis an astable, asymmetrical multivibrator adapted to supply current tosaid solenoid during the long-period portion of each oscillatory cycle,and adapted to supply current to the engaged contacts of said steppingswitch during the short-period portion of each oscillatory cycle.

23. The invention as claimed in claim 22, in which said means to supplycurrent to said solenoid includes,

an electrical power supply connected to energize said multivibrator, and

storage means responsive to said power supply for receiving and storingelectrical energy therefrom and for supplying such stored energy to saidmultivibrator to maintain theenergization thereof during periods of lossof power from said power supply.

24. The invention as claimed in claim 23 including means for providing aunidirectional 'low impedance path to ground for voltage steps that arecaused by said solenoid upon loss of power from said power supply. 25.The invention as claimed in claim 22, in which start-switch means areprovided for said multivibrator, and in which means are provided toinsure that said multivibrator starts to oscillate at the long-periodportion of the first cycle upon closing of said start-switch means, andalso to abbreviate greatly the duration of such long-period portion ofthe first cycle.

26. A method of operating an intervaiometer apparatus for firing a bankof rockets, such apparatus comprising a rotary switch driven by asolenoid-type stepping motor, said stepping motor efi'ecting shifting ofsaid switch from one switching position to the next switching positionupon each energization of said motor, said switch remaining stationaryupon each deenergization of said motor, which method comprises:

applying power to the solenoid of said motor for a time period longerthan that which is required to effect shifting of said switch from oneposition to the next, said time period being sufficiently long to insurethat the shocks and vibrations incident to the firing of the rockets insaid bank will dissipate while said solenoid is substantially fullyenergized! thereafter discontinuing the application of power to saidsolenoid for a time period shorter than said time period of powerapplication thereto, and

thereafter repeating in alternation said steps of applying power anddiscontinuing the same. I

27. The invention as claimed in claim 26, in which said method furthercomprises supplying rocket-firing current through said switch to one ofsaid rockets during said time period when supply of power to saidsolenoid is discontinued, but a sufficiently short time beforeapplication of power to said solenoid that said solenoid will beenergized before said shocks and vibrations reach said solenoid.

28. The invention as claimed in claim 27, in which each of said periodsduring which power is applied to said solenoid is on the order ofseveral times longer than each of said periods when no power is appliedthereto.

29. The invention as claimed in claim 28, in which each of said periodsof power application is about three times longer than each of saidperiods of no power application.

30. The invention as claimed in claim 26, in which said methodadditionally comprises employing a switch which is initially in a safetyposition at which none of the operative switch contacts are engaged witheach other, and in which said method further comprises supplying to saidsolenoid, in advance of the first-mentioned one of the specifiedapplications of power to said solenoid, a relatively short pulse ofpower adapted to rotate said switch from said safety position to thefirst operative position.

31. An intervalometer, which comprises:

a stepping switch,

a solenoid-type stepping motor connected to said switch to drive thesame,

a free-running multivibrator,

means responsive to the on condition of one side of said multivibratorto supply energizing pulses of current to the solenoid of said steppingmotor, and

means responsive to the on condition of the other side of saidmultivibrator to supply firing pulses of current to said switch and thusto the devices connected thereto.

32. The invention as claimed in claim 31, in which said switch isconnected to the firing devices in a rocket launcher, in which saidmultivibrator is an asymmetrical or unbalanced multivibrator, in whichsaid multivibrator and said means responsive to the on condition of saidone side supply relatively long-period pulses to said solenoid, and inwhich said means responsive to the on condition of said other sidesupply relatively short-period pulses to said switch.

33. The invention as claimed in claim 32, in which said multivibrator ishighly unbalanced, the degree of unbalance being such that said one sidethereof is in on condition at least several times as long as said otherside thereof.

34. The invention as claimed in claim 31, in which said multivibratorfurther incorporates means to perform both of the following functions:

a. cause said one side of said multivibrator to achieve the on conditionprior to the other side thereof, upon initiation of multivibratoraction, and

b. abbreviate the duration of the fast on" condition of said one side,upon initiation of multivibrator action, while leaving unabbreviated thedurations of subsequent on conditions of said one side.

35. The invention as claimed in claim 34 including an electrical powersupply connected to energize said multivibrator, and

storage means responsive to said power supply for receiving and storingelectrical energy therefrom and for supplying such stored energy to saidmultivibrator to maintain the energization thereof during periods ofloss of power from said power supply.

36. The invention as claimed in claim 27, wherein said motor includes asolenoid, and

means for providing a unidirectional low impedance path to ground forvoltage steps that are caused by said solenoid upon loss of power fromsaid power supply.

37. The invention as claimed in claim 34, in which said means is athreshold means, and in which said multivibrator is unbalanced, theunbalance being such that the durations of the second and subsequent on"conditions of said one side are substantially longer than the durationsof the on conditions of said other side.

38. The invention as claimed in claim 31, in which the time constants insaid multivibrator are such that the time required for each full cycleof operation, during the steady-state operation thereof, is in the rangeof about 40 milliseconds to about 60 milliseconds.

39. The invention as claimed in claim 38, in which said time constantsare such that said other side of said multivibrator is in on conditionfor about 15 milliseconds.

40. An electromechanical intervalometer adapted to effect firing of abank of rockets, which comprises:

an unregulated D.C. lead connected to the positive terminal of a DC.power source through a pilotoperated switch, a ground lead connected tothe negative terminal of such power source,

a regulated D.C. lead connected to said unregulated D.C. lead through abiasing resistor,

a zener diode connected between said regulated D.C.

lead and said ground lead,

a first NlN transistor the base of which is connected through a secondresistor to said regulated D.C. lead, the collector of said firsttransistor being connected through a third resistor to said unregulatedD.C. lead,

a second NPN transistor the base of which is connected to said regulatedD.C. lead through a fourth resistor, the emitter of said secondtransistor being connected through two series-related diodes to saidground lead, the anodes of said diodes being relatively adjacent saidemitter of said second transistor, the collector of said secondtransistor being connected through a fifth resistor to said regulatedD.C. lead,

a first capacitor connected between the base of said first transistorand the collector of said second transistor,

a second capacitor connected between the collector of said firsttransistor and the base of said second transistor,

a solenoidoperated stepping motor,

a rotary switch connected mechanically to said motor for drivingthereby, I

a third NPN transistor the base of which is connected to the emitter ofsaid first transistor, and the emitter of which is connected to saidground lead, the collector of said third transistor being connectedthrough the solenoid of said stepping motor to said unregulated D.C.lead, and

a fourth NPN transistor the base of which is connected to the junctionbetween said third resistor and the collector of said first transistor,the emitter of said fourth transistor being connected to said regulatedD.C. lead, the collector of said fourth transistor being connected tothe base of a fifth and PNP transistor, the emitter of said fifthtransistor being connected to said unregulated D.C. lead,

the collector of said fifth transistor being connected to the movablecontact of said rotary switch, the stationary contacts of said switchbeing respectively connected to rockets in said bank of rockets. 41. Theinvention as claimed in claim 40, in which a ripple switch is connectedbetween said unregulated D.C. lead and the junction between the emitterof said first transistor and the base of said third transistor.

42. The invention as claimed in claim 40, in which a capacitor isconnected between said ground lead and the collector of said secondtransistor.

43. The invention as claimed in claim 40, in which the time constantformed by the combination of said fourth resistor and said secondcapacitor is substantially larger than the time constant formed by thecombination of said second resistor and said first capacitor, wherebysaid first transistor is on for a relatively long portion of eachoscillatory cycle.

44. The invention as claimed in claim 40 in which an isolating diode isconnected between said power source and said biasing and thirdresistors, in which a first storage capacitor is connected between saidground lead and the side of said isolating diode that is connected tosaid resistors, in which a second storage capacitor is connected betweensaid ground lead and the collector of said second transistor, in whichsaid motor includes a solenoid coil, and in which a coil EMF shuntingdiode is connected between said ground lead and said solenoid coil.

45. An intervalometer for supplying firing pulses in timed relationshipto a bank of rockets or the like, which comprises:

a stepping switch operated by a solenoid,

means to apply actuating power to said solenoid for predetermined timeperiods and at predetermined intervals,

said stepping switch stepping from one station to the next upon each ofsaid power applications to said solenoid, and

means associated with said stepping switch to supply firing current todifferent rockets in the rocket bank connected to said stepping switch,thus firing such rockets,

the timing of said means for applying power to said solenoid beingcorrelated to the firing times and firing characteristics of saidrockets, and also to the distance between said rockets and saidsolenoid, in such manner that said solenoid is energized when the shocksand vibrations incident to the firings of said rockets are applied tosaid solenoid, whereby to prevent erratic firings of said rockets,

said means to apply said power to said solenoid including an electricalpower supply,

a timing circuit energized from said power supply for applying saidpower for the aforesaid periods, and

storage means responsive to said power supply for receiving and storingelectrical energy therefrom and for supplying such stored energy to saidtiming circuit to maintain the energization thereof during periods ofloss of power from said power supply.

46. An intervalometer for supplying firing pulses in timed relationshipto a bank of rockets or the like, which comprises: a stepping switchoperated by a solenoid, means to apply actuating power to said solenoidfor predetermined time periods and at predetermined intervals, saidstepping switch stepping from one station to the next upon each of saidpower applications to said solenoid, and means associated with saidstepping switch to supply firing current to different rockets in therocket bank connected to said stepping switch, thus firing such rockets,the timing of said means for applying power to said solenoid beingcorrelated to the firing times and firing characteristics of saidrockets, and also to the distance between said rockets and saidsolenoid, in such manner that said solenoid is energized when the shocksand vibrations incident to the firings of said rockets .are applied tosaid solenoid, whereby to prevent erratic firings of said rockets, saidmeans to apply said power to said solenoid operating to apply such powersufficiently soon after said supplying of firing current to said rocketsthat said solenoid is substantially fully energized when said shocks andvibrations reach said solenoid, said means to apply said power to saidsolenoid applying the same for time periods sufficiently long tomaintain said solenoid substantially fully energized until said shocksand vibrations are dissipated, and means for providing a unidirectionallow impedance path to ground for voltage steps that are caused by saidsolenoid upon loss of power from said power supply.

47. An intervalometer for supplying firing pulses in timed relationshipto a bank of rockets or the like, which comprises:

a stepping switch operated by a solenoid,

means to apply actuating power to said solenoid for predetermined timeperiods and at predetermined intervals,

said stepping switch stepping from one station to the next upon each ofsaid power applications to said solenoid, and

means associated with said stepping switch to supply firing current todifferent rockets in the rocket bank connected to said stepping switch,thus firing such rockets,

the timing of said means for applying power to said solenoid beingcorrelated to the firing times and firing characteristics of saidrockets, and also to the distance between said rockets and saidsolenoid, in such manner that said solenoid is energized when the shocksand vibrations incident to the things of said rockets are applied tosaid solenoid,

whereby to prevent erratic firings of said rockets,

said means to apply power to said solenoid applying thereto a firstpulse of current which is relatively short but still sufficiently longto effect retraction of the armature of said solenoid, thereafterdiscontinuing application of power to said solenoid for a relativelyshort time period, thereafter applying to said solenoid a second pulseof current which is much longer than said first pulse, thereafterdiscontinuing application of power to said solenoid for said relativelyshort time period, thereafter applying to said solenoid a third pulse ofcurrent which is much longer than said first pulse, and thereaftercontinuing to supply relatively long pulses of current followed byrelatively short periods of discontinuation of application of power tosaid solenoid,

said means to apply said power to said solenoid including an electricalpower supply,

a timing circuit energized from said power supply for applying saidpower for the aforesaid periods, and

storage means responsive to said power supply for receiving and storingelectrical energy therefrom and for supplying such stored energy to saidtiming circuit to maintain the energization thereof during periods ofloss of power from said power supply.

48. in an intervalometer for supplying firing pulses in timed relationto a bank of explosive devices, said intervalometer having a steppingswitch adapted to step from one position to another to successivelyapply firing pulses to different ones of said devices, singly or ingroups, thus firing said devices and producing shock and vibrationforces that are transmitted to said intervalometer during a known periodfollowing each such firing, a stepping switch drive motor armature, anda coil capable of being energized to shift the motor armature to a givenposition from which it is released when the coil is de-energized, theimprovement comprising timing means for repetitively and alternatelyenergizing said coil and feeding firing pulses to said devices throughsaid stepping switch, said timing means comprising:

means for delivering a relatively brief firing pulse to said steppingswitch,

means for delivering to said motor coil an energizing pulse thatinitiates energization of said coil at a time following said firingpulse that is less than the time required for said shock forces producedby said firing to be transmitted to said intervalometer, said lastmentioned means including means for maintaining said coil energizingpulse for a time at least equal to said knovm period whereby allsubstantial shocks and vibrations will dissipate before the coil isde-energized,

each said brief firing pulse being initiated during a time when saidcoil energizing pulse is absent, whereby said motor coil is energizedand said armature is held in position by energization of said coilduring the occurrence of shock and vibration resulting from said firing.

49. The intervalometer of claim 48 wherein the duration of saidenergizing pulse to said motor coil is considerably greater than theintervening time in which no pulse is supplied thereto whereby the motorcoil is fully energized and the armature is held the majority of thetime during each cycle of operation.

50. In an intervalometer for supplying firing pulses in timed relationto a bank of explosive devices, said intervalometer having a steppingswitch adapted to step from one position to another to successivelyapply firing pulses to different ones of said devices, singly or ingroups, thus firing said devices and producing shock and vibrationforces that are transmitted to said intervalometer durin a known periodfollowing such firing a stepping swltc drive motor armature, and a C01capable of being energized to shift and hold the motor armature in agiven position from which it is released when the coil is de-energized,the improvement c0mprising:

means for energizing said motor coil to hold said armature againstmovement immediately after each firing and before said shock andvibration forces are transmitted to said intervalometer, said meansincluding means for retaining energization of said coil and therebyretaining said armature in said held condition for a time substantiallyequal to said known period and sufficient to insure substantialdissipation of shock and vibration forces produced by said firing, andmeans for initiating firing and releasing the energization of said motorcoil, only after said shock and vibration forces having substantiallydissipated to thereby permit said armature to be moved.

1. An intervalometer for supplying firing pulses in timed relationshipto a bank of rockets or the like, which comprises: a stepping switchoperated by a solenoid, means to apply actuating power to said solenoidat predetermined intervals, said stepping switch stepping from onestation to the next upon each of said power applications to saidsolenoid, and means associated with said stepping switch to supplyfiring current to different rockets in the rocket bank connected to saidstepping switch, thus firing such rockets and generating shock forcesthat are applied to said intervalometer during a predetermined periodfollowing such firing, said means for applying power to said solenoidincluding timing means correlated to the firing times and firingcharacteristics of said rockets, and also to the distance between saidrockets and said solenoid, for maintaining said solenoid in energizedcondition throughout said predetermined period when the shocks andvibrations incident to the firings of said rockets are applied to saidsolenoid, whereby to prevent erratic firings of said rockets.
 2. Theinvention as claimed in claim 1, in which said means to supply firingcurrent to said rockets includes means for supplying such firing currentduring periods when there is no power applied to said solenoid.
 3. Theinvention as claimed in claim 2, in which said means to apply said powerto said solenoid includes means for applying such power sufficientlysoon after said supplying of firing current to said rockets that saidsolenoid is substantially fully energized when said shocks andvibrations reach said solenoid, and in which said means to apply saidpower to said solenoid includes means for applying the same for timeperiods sufficiently long to maintain said solenoid substantially fullyenergized until said shocks and vibrations are dissipated.
 4. Theinvention as claimed in claim 45 including unidirectional means forisolatIng said storage means from said solenoid and from said rocketfiring current.
 5. The invention as claimed in claim 1, in which saidmeans to apply power to said solenoid for predetermined time periods andat predetermined intervals includes means for energizing said solenoidwith a duty cycle of at least 50 percent.
 6. The invention as claimed inclaim 5, in which said duty cycle is in the range of 60 to 90 percent.7. The invention as claimed in claim 1, in which said means to applypower to said solenoid includes means for effecting application of suchpower thereto for an aggregate time longer than the aggregate timeduring which application of such power is discontinued, during eachfiring sequence of the intervalometer.
 8. The invention as claimed inclaim 7, in which said aggregate time during which such power is appliedto said solenoid is at least several times longer than said aggregatetime during which application of such power is discontinued.
 9. Theinvention as claimed in claim 1, in which said means to apply power tosaid solenoid includes means for maintaining the same substantiallyfully energized for a first period of time, means for discontinuingapplication of power to said solenoid for a second period of timeshorter than said first period of time, means for applying power to saidsolenoid for said first period of time, means for discontinuingapplication of power to said solenoid for said second period of timeshorter than said first period of time, and means for repeating saidlong-short relationship until completion of firing of said bank ofrockets.
 10. The invention as claimed in claim 9, in which said secondperiod of time has a duration which is much smaller than said firstperiod of time.
 11. The invention as claimed in claim 1, in which saidmeans to apply power to said solenoid includes means for applyingthereto a first pulse of current which is relatively short but stillsufficiently long to effect retraction of the armature of said solenoid,means for thereafter discontinuing application of power to said solenoidfor a relatively short time period, means for thereafter applying tosaid solenoid a second pulse of current which is much longer than saidfirst pulse, means for thereafter discontinuing application of power tosaid solenoid for said relatively short time period, means forthereafter applying to said solenoid a third pulse of current which ismuch longer than said first pulse, and means for thereafter continuingto supply relatively long pulses of current followed by relatively shortperiods of discontinuation of application of power to said solenoid. 12.The invention as claimed in claim 11, in which said means to supplyfiring current to said rockets includes means for supplying such firingcurrent during periods when there is no power applied to said solenoid.13. The invention as claimed in claim 1, in which said means to supplyfiring current to said rockets is a source of current pulses includingelectronic switching means external to said stepping switch.
 14. Anintervalometer for supplying firing pulses in timed relationship to abank of rockets or the like, which comprises: a stepping switch havingnumerous stationary contacts adapted to be engaged sequentially by amovable contact, each of said stationary contacts being connected to thefiring means for at least one rocket in said bank thereof, said movablecontact being initially in a safety position out of engagement with anyof said stationary contacts, a solenoid motor mechanism connected tosaid stepping switch and so related thereto that the first energizationof the solenoid in said mechanism effects shifting of said movablecontact from said safety position to a first position in engagement withthe first of said stationary contacts; the second energization of saidsolenoid effects shifting of said movable contact from said firstposition into a second position in engagement with the second of sAidstationary contacts, and subsequent energizations of said solenoideffect successive shifting of said movable contact into successivepositions in engagement with others of said stationary contacts, andmeans associated with said stepping switch and with said solenoid motormechanism to first supply to said solenoid a first current pulsesufficiently long to shift said movable contact from said safetyposition to said first position, to then send firing current throughsaid then-engaged movable contact and first stationary contact, to thensupply to said solenoid a second current pulse sufficiently long toshift said movable contact to said second position and also sufficientlylong to maintain said solenoid substantially fully energized throughoutthe time when the shocks and vibrations incident to firing of the rocketconnected to said first stationary contact are received by said steppingswitch and by said mechanism, to then send firing current through saidthen-engaged movable contact and second stationary contact, and to thenrepeat in alternation all of such steps of supplying current pulses tosaid solenoid and sending firing current through the engaged contacts,excepting the first-mentioned step of shifting said movable contact fromsaid safety position to said first position, whereby the rocket in saidbank are fired sequentially in a non-erratic manner.
 15. The inventionas claimed in claim 14, in which said last-named means effectsdiscontinuation of application of power to said solenoid for asubstantial time period after the end of each of said current pulsesthereto, during which time period said firing current is suppliedthrough the then-engaged contacts.
 16. The invention as claimed in claim15, in which said last-named means is so constructed that the durationof each of said second and subsequent pulses of current to said solenoidis substantially longer than the duration of the period during whichapplication of power to said solenoid is discontinued.
 17. The inventionas claimed in claim 16, in which said means to apply said pulses to saidsolenoid includes, an electrical power supply, a timing circuitenergized from said power supply for applying said pulses for theaforesaid periods, and storage means responsive to said power supply forreceiving and storing electrical energy therefrom and for supplying suchstored energy to said timing circuit to maintain the energizationthereof during periods of loss of power from said power supply.
 18. Theinvention as claimed in claim 16, in which the duration of each of saidsecond and subsequent pulses is on the order of several times longerthan the duration of each period of discontinuation of application ofpower to said solenoid.
 19. The invention as claimed in claim 14, inwhich said last-named means effects discontinuation of said firstcurrent pulse to said solenoid a relatively short time period aftercommencement thereof, said short time period being barely sufficient toinsure stepping of said movable contact from said safety position tosaid first position, said short time period having a duration muchshorter than that of said second and subsequent current pulses to saidsolenoid.
 20. The invention as claimed in claim 14, in which saidlast-named means supplies said current pulses to said solenoidsufficiently soon after sending of said firing current to insure thatsaid solenoid is substantially fully energized when said shocks andvibrations reach said solenoid, and in which said last-named meansdelivers said current pulses to said solenoid throughout time periodssufficiently long to insure that said shocks and vibrations aredissipated before said solenoid is de-energized.
 21. The invention asclaimed in claim 14, in which said last-named means is an electroniccircuit incorporating electronic switching means to supply said currentpulses to said solenoid, and also incorporating electronic switchingmeans to supply firing current to said rocket bank through the engagedcontacts of said stepping switch, said first-mentioned andsecond-mentioned electronic switching means operating in alternation tosupply said current pulses to said solenoid and to supply said firingcurrent to said rocket bank.
 22. The invention as claimed in claim 14,in which said last-named means is an astable, asymmetrical multivibratoradapted to supply current to said solenoid during the long-periodportion of each oscillatory cycle, and adapted to supply current to theengaged contacts of said stepping switch during the short-period portionof each oscillatory cycle.
 23. The invention as claimed in claim 22, inwhich said means to supply current to said solenoid includes, anelectrical power supply connected to energize said multivibrator, andstorage means responsive to said power supply for receiving and storingelectrical energy therefrom and for supplying such stored energy to saidmultivibrator to maintain the energization thereof during periods ofloss of power from said power supply.
 24. The invention as claimed inclaim 23 including means for providing a unidirectional low impedancepath to ground for voltage steps that are caused by said solenoid uponloss of power from said power supply.
 25. The invention as claimed inclaim 22, in which start-switch means are provided for saidmultivibrator, and in which means are provided to insure that saidmultivibrator starts to oscillate at the long-period portion of thefirst cycle upon closing of said start-switch means, and also toabbreviate greatly the duration of such long-period portion of the firstcycle.
 26. A method of operating an intervalometer apparatus for firinga bank of rockets, such apparatus comprising a rotary switch driven by asolenoid-type stepping motor, said stepping motor effecting shifting ofsaid switch from one switching position to the next switching positionupon each energization of said motor, said switch remaining stationaryupon each de-energization of said motor, which method comprises:applying power to the solenoid of said motor for a time period longerthan that which is required to effect shifting of said switch from oneposition to the next, said time period being sufficiently long to insurethat the shocks and vibrations incident to the firing of the rockets insaid bank will dissipate while said solenoid is substantially fullyenergized, thereafter discontinuing the application of power to saidsolenoid for a time period shorter than said time period of powerapplication thereto, and thereafter repeating in alternation said stepsof applying power and discontinuing the same.
 27. The invention asclaimed in claim 26, in which said method further comprises supplyingrocket-firing current through said switch to one of said rockets duringsaid time period when supply of power to said solenoid is discontinued,but a sufficiently short time before application of power to saidsolenoid that said solenoid will be energized before said shocks andvibrations reach said solenoid.
 28. The invention as claimed in claim27, in which each of said periods during which power is applied to saidsolenoid is on the order of several times longer than each of saidperiods when no power is applied thereto.
 29. The invention as claimedin claim 28, in which each of said periods of power application is aboutthree times longer than each of said periods of no power application.30. The invention as claimed in claim 26, in which said methodadditionally comprises employing a switch which is initially in a safetyposition at which none of the operative switch contacts are engaged witheach other, and in which said method further comprises supplying to saidsolenoid, in advance of the first-mentioned one of the specifiedapplications of power to said solenoid, a relatively short pulse ofpower adapted to rotate said switch from said safety position to thefirst operative position.
 31. An intervalometEr, which comprises: astepping switch, a solenoid-type stepping motor connected to said switchto drive the same, a free-running multivibrator, means responsive to the''''on'''' condition of one side of said multivibrator to supplyenergizing pulses of current to the solenoid of said stepping motor, andmeans responsive to the ''''on'''' condition of the other side of saidmultivibrator to supply firing pulses of current to said switch and thusto the devices connected thereto.
 32. The invention as claimed in claim31, in which said switch is connected to the firing devices in a rocketlauncher, in which said multivibrator is an asymmetrical or unbalancedmultivibrator, in which said multivibrator and said means responsive tothe ''''on'''' condition of said one side supply relatively long-periodpulses to said solenoid, and in which said means responsive to the''''on'''' condition of said other side supply relatively short-periodpulses to said switch.
 33. The invention as claimed in claim 32, inwhich said multivibrator is highly unbalanced, the degree of unbalancebeing such that said one side thereof is in ''''on'''' condition atleast several times as long as said other side thereof.
 34. Theinvention as claimed in claim 31, in which said multivibrator furtherincorporates means to perform both of the following functions: a. causesaid one side of said multivibrator to achieve the ''''on'''' conditionprior to the other side thereof, upon initiation of multivibratoraction, and b. abbreviate the duration of the first ''''on'''' conditionof said one side, upon initiation of multivibrator action, while leavingunabbreviated the durations of subsequent ''''on'''' conditions of saidone side.
 35. The invention as claimed in claim 34 including anelectrical power supply connected to energize said multivibrator, andstorage means responsive to said power supply for receiving and storingelectrical energy therefrom and for supplying such stored energy to saidmultivibrator to maintain the energization thereof during periods ofloss of power from said power supply.
 36. The invention as claimed inclaim 27, wherein said motor includes a solenoid, and means forproviding a unidirectional low impedance path to ground for voltagesteps that are caused by said solenoid upon loss of power from saidpower supply.
 37. The invention as claimed in claim 34, in which saidmeans is a threshold means, and in which said multivibrator isunbalanced, the unbalance being such that the durations of the secondand subsequent ''''on'''' conditions of said one side are substantiallylonger than the durations of the ''''on'''' conditions of said otherside.
 38. The invention as claimed in claim 31, in which the timeconstants in said multivibrator are such that the time required for eachfull cycle of operation, during the steady-state operation thereof, isin the range of about 40 milliseconds to about 60 milliseconds.
 39. Theinvention as claimed in claim 38, in which said time constants are suchthat said other side of said multivibrator is in ''''on'''' conditionfor about 15 milliseconds.
 40. An electromechanical intervalometeradapted to effect firing of a bank of rockets, which comprises: anunregulated D.C. lead connected to the positive terminal of a D.C. powersource through a pilot-operated switch, a ground lead connected to thenegative terminal of such power source, a regulated D.C. lead connectedto said unregulated D.C. lead through a biasing resistor, a zener diodeconnected between said regulated D.C. lead and said ground lead, a firstNPN transistor the base of which is connected through a second resistorto said regulated D.C. lead, the collector of said first transistorbeing connected through a third resistor to said unregulated D.C. lead,a second NPN transistor the base of which is connected To said regulatedD.C. lead through a fourth resistor, the emitter of said secondtransistor being connected through two series-related diodes to saidground lead, the anodes of said diodes being relatively adjacent saidemitter of said second transistor, the collector of said secondtransistor being connected through a fifth resistor to said regulatedD.C. lead, a first capacitor connected between the base of said firsttransistor and the collector of said second transistor, a secondcapacitor connected between the collector of said first transistor andthe base of said second transistor, a solenoid-operated stepping motor,a rotary switch connected mechanically to said motor for drivingthereby, a third NPN transistor the base of which is connected to theemitter of said first transistor, and the emitter of which is connectedto said ground lead, the collector of said third transistor beingconnected through the solenoid of said stepping motor to saidunregulated D.C. lead, and a fourth NPN transistor the base of which isconnected to the junction between said third resistor and the collectorof said first transistor, the emitter of said fourth transistor beingconnected to said regulated D.C. lead, the collector of said fourthtransistor being connected to the base of a fifth and PNP transistor,the emitter of said fifth transistor being connected to said unregulatedD.C. lead, the collector of said fifth transistor being connected to themovable contact of said rotary switch, the stationary contacts of saidswitch being respectively connected to rockets in said bank of rockets.41. The invention as claimed in claim 40, in which a ripple switch isconnected between said unregulated D.C. lead and the junction betweenthe emitter of said first transistor and the base of said thirdtransistor.
 42. The invention as claimed in claim 40, in which acapacitor is connected between said ground lead and the collector ofsaid second transistor.
 43. The invention as claimed in claim 40, inwhich the time constant formed by the combination of said fourthresistor and said second capacitor is substantially larger than the timeconstant formed by the combination of said second resistor and saidfirst capacitor, whereby said first transistor is on for a relativelylong portion of each oscillatory cycle.
 44. The invention as claimed inclaim 40 in which an isolating diode is connected between said powersource and said biasing and third resistors, in which a first storagecapacitor is connected between said ground lead and the side of saidisolating diode that is connected to said resistors, in which a secondstorage capacitor is connected between said ground lead and thecollector of said second transistor, in which said motor includes asolenoid coil, and in which a coil EMF shunting diode is connectedbetween said ground lead and said solenoid coil.
 45. An intervalometerfor supplying firing pulses in timed relationship to a bank of rocketsor the like, which comprises: a stepping switch operated by a solenoid,means to apply actuating power to said solenoid for predetermined timeperiods and at predetermined intervals, said stepping switch steppingfrom one station to the next upon each of said power applications tosaid solenoid, and means associated with said stepping switch to supplyfiring current to different rockets in the rocket bank connected to saidstepping switch, thus firing such rockets, the timing of said means forapplying power to said solenoid being correlated to the firing times andfiring characteristics of said rockets, and also to the distance betweensaid rockets and said solenoid, in such manner that said solenoid isenergized when the shocks and vibrations incident to the firings of saidrockets are applied to said solenoid, whereby to prevent erratic firingsof said rockets, said means to apply said power to said soleNoidincluding an electrical power supply, a timing circuit energized fromsaid power supply for applying said power for the aforesaid periods, andstorage means responsive to said power supply for receiving and storingelectrical energy therefrom and for supplying such stored energy to saidtiming circuit to maintain the energization thereof during periods ofloss of power from said power supply.
 46. An intervalometer forsupplying firing pulses in timed relationship to a bank of rockets orthe like, which comprises: a stepping switch operated by a solenoid,means to apply actuating power to said solenoid for predetermined timeperiods and at predetermined intervals, said stepping switch steppingfrom one station to the next upon each of said power applications tosaid solenoid, and means associated with said stepping switch to supplyfiring current to different rockets in the rocket bank connected to saidstepping switch, thus firing such rockets, the timing of said means forapplying power to said solenoid being correlated to the firing times andfiring characteristics of said rockets, and also to the distance betweensaid rockets and said solenoid, in such manner that said solenoid isenergized when the shocks and vibrations incident to the firings of saidrockets are applied to said solenoid, whereby to prevent erratic firingsof said rockets, said means to apply said power to said solenoidoperating to apply such power sufficiently soon after said supplying offiring current to said rockets that said solenoid is substantially fullyenergized when said shocks and vibrations reach said solenoid, saidmeans to apply said power to said solenoid applying the same for timeperiods sufficiently long to maintain said solenoid substantially fullyenergized until said shocks and vibrations are dissipated, and means forproviding a unidirectional low impedance path to ground for voltagesteps that are caused by said solenoid upon loss of power from saidpower supply.
 47. An intervalometer for supplying firing pulses in timedrelationship to a bank of rockets or the like, which comprises: astepping switch operated by a solenoid, means to apply actuating powerto said solenoid for predetermined time periods and at predeterminedintervals, said stepping switch stepping from one station to the nextupon each of said power applications to said solenoid, and meansassociated with said stepping switch to supply firing current todifferent rockets in the rocket bank connected to said stepping switch,thus firing such rockets, the timing of said means for applying power tosaid solenoid being correlated to the firing times and firingcharacteristics of said rockets, and also to the distance between saidrockets and said solenoid, in such manner that said solenoid isenergized when the shocks and vibrations incident to the firings of saidrockets are applied to said solenoid, whereby to prevent erratic firingsof said rockets, said means to apply power to said solenoid applyingthereto a first pulse of current which is relatively short but stillsufficiently long to effect retraction of the armature of said solenoid,thereafter discontinuing application of power to said solenoid for arelatively short time period, thereafter applying to said solenoid asecond pulse of current which is much longer than said first pulse,thereafter discontinuing application of power to said solenoid for saidrelatively short time period, thereafter applying to said solenoid athird pulse of current which is much longer than said first pulse, andthereafter continuing to supply relatively long pulses of currentfollowed by relatively short periods of discontinuation of applicationof power to said solenoid, said means to apply said power to saidsolenoid including an electrical power supply, a timing circuitenergized from said power supply for applying said power for theaforesaid periods, and storage means responsive to said power supply Forreceiving and storing electrical energy therefrom and for supplying suchstored energy to said timing circuit to maintain the energizationthereof during periods of loss of power from said power supply.
 48. Inan intervalometer for supplying firing pulses in timed relation to abank of explosive devices, said intervalometer having a stepping switchadapted to step from one position to another to successively applyfiring pulses to different ones of said devices, singly or in groups,thus firing said devices and producing shock and vibration forces thatare transmitted to said intervalometer during a known period followingeach such firing, a stepping switch drive motor armature, and a coilcapable of being energized to shift the motor armature to a givenposition from which it is released when the coil is de-energized, theimprovement comprising timing means for repetitively and alternatelyenergizing said coil and feeding firing pulses to said devices throughsaid stepping switch, said timing means comprising: means for deliveringa relatively brief firing pulse to said stepping switch, means fordelivering to said motor coil an energizing pulse that initiatesenergization of said coil at a time following said firing pulse that isless than the time required for said shock forces produced by saidfiring to be transmitted to said intervalometer, said last mentionedmeans including means for maintaining said coil energizing pulse for atime at least equal to said known period whereby all substantial shocksand vibrations will dissipate before the coil is de-energized, each saidbrief firing pulse being initiated during a time when said coilenergizing pulse is absent, whereby said motor coil is energized andsaid armature is held in position by energization of said coil duringthe occurrence of shock and vibration resulting from said firing. 49.The intervalometer of claim 48 wherein the duration of said energizingpulse to said motor coil is considerably greater than the interveningtime in which no pulse is supplied thereto whereby the motor coil isfully energized and the armature is held the majority of the time duringeach cycle of operation.
 50. In an intervalometer for supplying firingpulses in timed relation to a bank of explosive devices, saidintervalometer having a stepping switch adapted to step from oneposition to another to successively apply firing pulses to differentones of said devices, singly or in groups, thus firing said devices andproducing shock and vibration forces that are transmitted to saidintervalometer during a known period following such firing, a steppingswitch drive motor armature, and a coil capable of being energized toshift and hold the motor armature in a given position from which it isreleased when the coil is de-energized, the improvement comprising:means for energizing said motor coil to hold said armature againstmovement immediately after each firing and before said shock andvibration forces are transmitted to said intervalometer, said meansincluding means for retaining energization of said coil and therebyretaining said armature in said held condition for a time substantiallyequal to said known period and sufficient to insure substantialdissipation of shock and vibration forces produced by said firing, andmeans for initiating firing and releasing the energization of said motorcoil, only after said shock and vibration forces having substantiallydissipated to thereby permit said armature to be moved.